Apparatus for aiming guns



May 7, 1946. 1. w. DOYLE ErAl. 2,399,726

APPARATUS FOR AIMING GUNS Filed March 11, 1940 10 Sheets-sheet 1 May 7, 1946. l. w. DoYLE E1-AL 2,399,726

APPARATUS FOR AIMING GUNS Filed March' 11, 1940 10 Sheets-Sheet 2 vv: vl v uw "Y INVEN [ORS H Ronge 2:52. :1s/A"- Irving Wi ,Dm/Le l2, Relative Motion BY HEzwin Haie {95 \L97 1"237 @Q WY/{QW HORIZONTAL oEFLEcTnoN cu'gmnj ^TT0RNEY$ May 7, 1946. l. w. DoYLE 'E1-AL 2,399,726

APPARATUS FOR AIMING GUNS Filed March 11, 1940 l0 Sheets-Sheet 3 NVENTORS 260 [ruling W D0 le BY H. Erwin Ha e @Ll/L,

' i TToRNEYs May '7, 1946. l. w. DoY| E Erm. 2,399,726

APPARATUS FOR AIMINC- GUNS V Fl'ed March 11, 1940 10 Sheets-Sheet 4 Z0\'.'T. El

ATTORNE s May 7, 1946. l. w. DOYLE ETAL 2,399,726

APPARATUS FOR AIMING GUNS Filed Maren 11, 1940l 1o sheets-sheet 5 TEN' E* .250

ZENITH INVENTORS ving WT D0 BY H. Erwin Ha(e ATTORNEYS May 7, 1946. 1. w. DOYLE ErAL 2,399,726

APPARATUS FOR AIMING GUNS Filed Marchl 11, 1940 l0 Sheets-Sheet 6 HH Illl Il HI 182 INVENTORS Irving Wal/IC Bv H. Erwin flair' May 7, 1946. l. w. DOYLE x-:rAL

APPARATUS FOR AIMING GUNS Fi'led March 11, 1940 l0 Sheets-Sheet 7 #New O DH? Vl @mn/E O .L vN Tqw. N T wmEm/n myn. ,A L V.. B 2 w 7J 1o sheets-sheet 9 l. W. DOYLE ETAL APPARATUS FOR AIMING GUNS Filed March 1l, 1940 May 7, 1946. w. DoYLE: ETAL l 2,399,726

APPARATUS FOR AIMING GUNS Filed Mar'ch 11, 1940 1o sheets-sheet 1o IN ENTO S Irugng VDOyle Y HErwin Hale ATTORN YS Patented May 7, 1946 APPARATUS Fon AIMING GUNS Irving W. Doyle, Amityville, and Henry Erwin Hale, Freeport, N. Y., assignors to Fairchild Camera and Instrument Corporation, a corporation oi' Delaware Application March 11, 1940, Serial No. 323,474

16 Claims.

This invention relates to a. method of and ap paratus for aiming a gun, and more particularly for aiming a, machine gun or cannon at a target as the gun and target move relatively.

It is among the objects of this invention to provide a method of and apparatus for sighting a gun, by which the aim of the gun -is automatically corrected to compensate for various factors which affect the course of aprojectiie. Other objects will be in part apparent.- and in part pointed out hereinafter.

The invention accordingly consists in the features of construction. combinations of elements. arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others. all as will be illustratively described herein. and the scope of the application oi' which will be indicated in the following claims.

In the drawings, wherein there are shown several embodiments of our invention.

Figure 1 is a schematic view of a portion of our apparatus, together with a control circuit therefor:

Figure 2 is a view similar to Figure 1, but showing a modied control circuit;

Figure 3 is a sectional elevation of a bomber turret wherein our apparatus is mounted;

Figure 4 is a plan view of the bomber turret and gun aiming apparatus;

Figure 5 is an enlarged elevation of a portion of a machine gun mount incorporating certain structural features of our apparatus:

Figure 6 is a fragmentary rear elevation, partly in section, of the apparatus of Figure 5;

Figure 7 is a bottom plan view taken along the line 1-1 of Figure 3;

Figure 8 is an enlarged sectional elevation taken along the line B-l of Figure '7;

Figure 9 is an elevation. partly in section, taken along the line 9 9 of Figure 7;

Figure l0 is an enlarged plan view indicated by the line Ill-I0 oi Figure 3:

Figure 11 is an elevation of Figure 10;

Figure l2 is an enlarged sectional elevation taken along the line l2-l2 of Figure 4;

Figure 13 is a sectional view taken along the line |3-l3 of Figure 12;

Figure 14 is an enlarged sectional elevation taken along the line II-Id of Figure 4;

Figure 15 is a sectional elevation of a turret having mounted therein a modified form of our apparatus; and,

Figure i6 is a top plan view of the apparatus shown in Figure i5.

Similar reference characters refer to similar parts throughout the various views of the drawings.

To facilitate an understanding hereof, and to expedite the description, the invention will be considered hereafter as applied only to machine guns adapted to be movably mounted on aircraft such as bombers or dirigibles, it being understood, however, that the invention s applicable to field guns of a caliber larger than that of machine guns. and to various other types of guns such as naval cannon and anti-aircraft guns adapted to shell moving targets.

Conventional aerial machine gun sights have undergone little change or improvement for a number of years, and are principally characterized by a number of concentric rings mounted on the gun barrel at a distance from its muzzle, the muzzle end of the barrel having a bead, or sometimes a pantagraphic device. In aiming the gun by a sight of this character, the gunner, in establishing his line of sight, estimates the range of his target, the elevation to attain correct projectile trajectory, and such other factors as enter into the aiming of the gun, and approximates a position within the concentric rings with which he aligns the bead and target. Obviously there is more guesswork and human skill involved in accurately aiming the gun with a sight of this character than there is mathematical certainty that the target will be hit. It is for this reason that the proportion of hits in target practice or in actual combat is small.

There are a number of factors in aerial gunnery which cause horizontal and vertical components of deviation between the line of fire and the line of sight of the gun, and which must be compensated for in aiming the gun to effect coincidence of bullet and target. These factors will hereinafter be referred to as:

l. Lead, or relative motion, i. e. the line of fire must be at an angle to the line of sight when there is relative motion between the gun and target so that the gun leads its target.

2. Trajectory, or superelevation, i. e. the superelevation, excluding air stream eects, of the gun necessary at the instant of fire to effect coincidence of bullet and target.

3. Bullet jump, i. e. as a bullet emerges from the gun barrel, the riing therein imparts spin to the bullet, the bullet thus having a gyroscopc action which, when the air stream hits the bullet, causes it to precess in a direction normal to the air stream or direction of force applied, except when the gun is firing straight into or with the air stream.

4. Windage, i. e. the horizontal deflection of the bullet from its true line of flight when the gun is moving at a substantial velocity due to the air stream rushing past the gun muzzle when the gun is firing in any direction except one coaxial with its path of movement.

The values of these factors of relative motion, trajectory, bullet jump and windage are determined by the factors of l. Range (instantaneous distance between gun and target) 2. Zenith position (angle between zenith and gun) 3. Azimuth position (clockwise angle between line of night and line of re) 4. Indicated air speed (hereafter referred to as IAS) 5. Altitude (air density) These latter ve factors are effective singly or in combination in determining the values of horizontal and vertical components of relative motion. trajectory, bullet jump and windage, as follows:

A. Vertical component l. Lead (relative motion) a. Range b. Altitude 2. Trajectory a. Range b. Zenith position 3. Bullet jump a. IAS

b. Azimuth position (zero effect when tiring fore and aft) c. Altitude 4. Windage a. IAB

b. Azimuth position (zero vertical component eect when firing dead abeam) c. Zenith position (zero vertical component effect when firing in horlzontal plane) d. Range e. Altitude B. Horizontal component 1. Lead (relative motion) a. Range b. Zenith position c. Altitude 2. Bullet jump a. IAS

b. Azimuth position (zero effect when firing dead abeam) c. Zenith position (zero effect when liring in horizontal plane) d. Altitude 3. Wlndage a. IAS

b. Azimuth position (zero effect when firing fore and aft) c. Range d. Altitude By way of illustration. let us assume that the gun plane is flying due south at an altitude of 2,000 feet and the target plane is also ilying due south on a parallel course at an altitude of 2.500 feet, that the two courses of the planes are displaced laterally 1,500 feet, and that ilrlng commences when the planes are 1,000- feet apart horizontally. This set of conditions brings into effect both the vertical and horizontal components of relative motion, trajectory (there is no horizontal component of deviation in compensating the line of re for trajectory), bullet jump and windage. Under these conditions, at the instant of re, when properly aimed, the gun points upwardly, forwardly and abeam of the gun plane. Hence the line of fire must be corrected with respect to the line of sight oi the gun l. To lead the target (allow for the relative motion of the two planes,

2. To compensate for the vertical component of trajectory occasioned by the superelevation of the gun and range of the target,

3. To compensate for the vertical and horizontal 'components of bullet jump occasioned by IAS, the deviation of the line of fire from both the vertical and horizontal, and

4. To compensate for the vertical and horizontal components of windage occasioned by IAS. the deviation of the line of re from both the vertical and horizontal, range and altitude.

The corrected line of fire is accordingly the resultant of the several vertical and horizontal components modied by the range of the target and the altitude of combat. It is this complex resultant which is beyond human ability to attain with such a degree of accuracy as to effect efiicient gunnery, particularly under stress of combat firing.

Many modern bombers which can readily attain speeds well in excess of 200 miles per hour, are equipped with various types of turrets in which machine guns are mounted. Some of these turrets are of the retractable type, extendible from the planes fuselage. Others take the form of blister-like protrusions pivoted from the fuselage. so that the turret gun is capable of a certain amount of universal motion relative to the fuselage. Further t0 facilitate the purposes and understanding hereof, the description will be conned to that type of turret which is extendible from the plane fuselage, rotatable relative thereto, and in which a gun is mounted for pivotal movement in vertical planes so that the gun muzzle is movable substantially universally within limits defined by such portions oi thc airplane structure as lie within the line ol fire of thc gun. The structural features of such a gun mount will be described in detail hereinbelow.

By way of generally describing the structurc which embodies our invention, it is first to bc noted that in one form of our apparatus a telescopic sight, preferably of the range finder type, is secured to the gun and related to the gun turret in such a manner that its horizontal and vertical components of movement are identical to those of the gun, e. the gun and sight move as a unit. At a focal plane within the range finder is a retlcle composed of vertical and horizontal cross hairs, respectively attached to galvanometer needles so as to move therewith. Accordingly at the point where the hairs cross, a reference mark capable of universal planar movement is established which with the target comprises the line of sight of the gun which can deviate relative to the line of re thereof. as will be described. As the lines of sight and fire do deviate, and as their deviation varies under certain circumstances, it will appear from the above that the deviation is proportional to the factors of lead. trajectory, bullet jump and windage. The eld of view of the range finder sight being substantially larger in area than the target plane, accordingly affords a sighting area about which the cross hairs of the reticle can be moved by the gunner, as will be described below, until the cross hairs are on the target, at which time the gun is accurately aimed.

Movement of the rectile is effected by current input to the galvanometers, current for the galvanometer controlling the vertical cross hair, which determines horizontal deiiection, being .sup` plied from a generator geared to the turret for operation thereby. Current for the galvanomcter controlling the horizontal cross hair, which determines vertical deflection, is supplied by another generator, geared to the gun or range under in such a manner that vertical movement thereof operates its generator. Hence two control circuits are involved, one hereafter referred to as the horizontal deection circuit, which is energized by rotation of the turret, and the other the vertical deection circuit, which is energized by vertical pivotal movement of the gun.

From the above, it may be seen that the generator outputs are respectively proportional to the horizontal and vertical components of angular velocity of the line of sight relative to fixed axes in space as the gunner keeps his sight trained on a moving target. If, of course, the gun and target were stationary and the trajectory of the bullet were at. there would be no necessity to move either the line of sight or the line of fire, and the two would coincide. Where, however, there is relative motion between gun and target as where one airplane is firing at another. a continued deviation of the line of sight is necessary to keep it on the target. As pointed out above, this movement of the line of sight is utllized to generate electrical energy.

Also as noted above the generator outputs are used to move the horizontal and vertical cross hairs which form the reticle. These voltages being proportional to the vertical and horizontal components of the angular velocity of the line oi sight only, are not compensated for the factors of lead, trajectory, bullet jump and wlndage, and accordingly must be modified in accordance therewith if the correct deviation between the lines of sight and fire is to be attained so as to aim the gun accurately.

Accordingly we modify the voltage of the vertical deflection circuit as follows:

l. For lead-An attenuaior is connected across the generator and mechanically connected to the adjustment on the range finder. As the range inder is adjusted the resistance of the attenuator is varied so that the generator output voltage is varied by an amount proportional to the range of the instant of gun nre. A second attenuator is connected across the generator and is adjusted in accordance with the altitude. Hence, the total generator output is an approximate function of time of night.

2. F01 tTaiect0ry.-Additional voltage is added to the circuit as by a battery, and this added voltage is metered into the circuit by at least two attenuators. one whose resistance is adjusted b v the range finder adjustment, and the other whose resistance is varied by an amount proportional to the zenith position of the line of ire. The latter attenuator is connected mechanically or otherwise to the sight or the gun so that vertical movement thereof varies the resistance.

3, The bullet jump-Additional voltage is added to the circuit and this added voltage is metered into the circuit by at least three attenuators. The resistance of the first is adjusted, by hand, ii' desired from a reading on a voltmcter calibrated in miles per hour so that the resist` ance is proportional to indicated air speed (IAS). The resistance of the second attenuator is adjusted by a cam or other mechanism operated by the gun, sight or turret during horizontal movement, thereof so that the vertical component of bullet jump is proportional to the horizontal deviation of the line of nre from the longitudinal axis of the airplane. The resistance of the third attenuator is adjusted in accordance with altitude. When the line of lire is fore or aft of the airplane ina horizontal plane, the vertical component of bullet jump is zero.

4. For wndage.-Additional voltage is added to the circuit, and th added voltage is metered into the circuit by five attenuators, so that the value ofthe voltage added is a. product of several voltages of the several attenuatrs. The resistances of these attenuators are adjusted in accordance with IAS, azimuth position, zenith p0- sition, range and altitude, so that the vertical component of windage may be said to be proportional to these several factors.

The value of the vertical deiiection voltage is impressed on the galvanometer which controls the horizontal cross hair so that the horizontal crass hair is moved to a. position which effects deviation of the line of lire of the gun from the line of sight in such a manner that the vertical component of angular velocity of the line of ire is proportional to the vertical component of linear velocity of the target. Hence, the line of fire of the,` gun is caused to correctly lead the target in so far as the vertical component of lead is concerned.

The voltage of the horizontal deflection circuit is modified as follows:

l. For lead, or relative moton.-An attenuator. whose resistance is varied by the range finder adlustment, is connected across the generator so that the output thereof is proportional to the range. Furthermore, the horizontal component of lead or relative motion is cil'ected by the vertical position of the gun. Hence, an attcnuator, the resistance of which is varied according to the gun's zenith position is also connected across the generator further to modify its output. As altitude i5 a factor here, a third attenuator adjusted in accordance with altitude is connected across the generator.

2. For bullet jump-Additional voltage is added to the circuit and the value of this voltage is determined by the product of the outputs of at least four attenuators, the resistances of which are respectively adjusted in accordance with indicated air speed, am'muth position, zenith posi tion and altitude. Hence, the component of horizontal deflection of the line of sight to compensate for bullet lump is proportional to IAS, azimuth and zenith positions and altitude, as stated.

3. For whatwe- Additional current is added to the circuit and the voltage of this current is a product of the voltages of at least four attenuators whose reslstances are varied respectively.

according to indicated air speed. horizontal position, range and altitude.

The horizontal deflection voltage is impressed on the second galvanometer which controls the position of the vertical cross hair, so that when the line of sight is van'ed to set the vertical cross hair on the target. the correct deviation i5 imparted to the line of fire so as to impart thereto the proper component of horizontal deflection. and hence to compensate the line of fire for the several factors which affect it. Hence, the horizontai component of angular velocity of the line of sight imparts to the line of re a horizontal component of angular velocity which is in turn proportional to the horizontal component of linear velocity of the target. The resultant of the horizontal and vertical components of angular velocity of the line of fire, as determined by the similar components of angular velocity of the line of sight, is proportional to the resultant of the horizontal and vertical components of linear velocityV of the target so that the line of lire leads the target by a correct amount.

In other words. when the gunner sights his target, he moves his range ilnder, and accordingly his gun. until the reticle formed by the cross hairs is on the target. This movement. as described above, energizes the two circuits, causing movement of the retlcle so as to cause deviation between the line of sight and line of fire, which deviation accurately aims the line of fire so as to impart thereto a lead which is corrected for the several factors which must be compensated for if bullet and target are to meet.

It should be noted, however, that in a system as above described, the angular velocity of the lines of iire and sight is not necessarily constant.

but might well be accelerating. in which case the angle of deflection between the gun and the line of sight will be increasing. Under such circumstances, the line of sight moves backward with respect to the line of fire by an amount which is proportional to the angular acceleration of the line of re or the gun, i, e. the rate of change of angular velocity of the line of fire. Therefore.,

the angular velocity of the line of sight is the algebraic sum of the instantaneous angular velocity of the line of fire, plus the backward instantaneous angular velocity of the line of sight with respect to the line of fire. The correct dcflection between the line of sight and the line of re should be proportional to the angular velocity of the line of sight, but the actual deection is proportional to the angular velocity of the gun. Therefore, an error is introduced in this deflection which is proportional to the angular velocity of the line of sight relative to the gun, and which is also proportional to the rate of change of anguiar velocity of the gun. To compensate or correct for this error. voltages are introduced into the horizontal and vertical deflection circuits in the opposite direction to that of the current flowing therein as a result of gun movement, and this counter E. M. F. is proportional to the rate of change of angular velocity of the gun. This counter E. M. F. may be introduced in each circuit as by a suitable self inductance, such as a. choke coil, the number of effective turns of which are preferably varied in accordance with varia tions in range and altitude, so that the counter E. M. F. is proportional to time of night.

Referring now to Figure l, wherein there is schematically shown a movably mounted gun. vertical and horizontal deflection control circuits which are energized in accordance with gun movement. and a reticle. the movement of which is responsive to the control circuit's energization, the gun is generally indicated at 20 and is mounted on a suitable horizontal support 2i capable of rotation in a horizontal plane. The gun is also pivoted to a vertical support 22 extending upwardly from support 2i for movement in vertical planes. A gear sector 23 is secured to gun 20 for operation of a train oi gears generally indicated at 24. connected to a. generator 25. Support 2i may have teeth cut therein for operation of a train of gears generally indicated at 26, con nected to a generator 2l. Generator 25 energizes the vertical deflection circuit, whereas generator 2l energizes the horizontal deflection circuit.

Vertical deflection circuit l. Relative motion-A pair of lines 26 and 29 are connected to the opposite sides of generator 25,-and lead to opposite sides of an attenuator 30, being connected to terminals 3i and 32 of the attenuator resistance 33. Attenuator 30 includes a slider arm 34 adapted to slide along resistance 33 to vary the generator output, and as arm 34 is connected to the range tindex' adjustment referred to hereinabove and described below, the value of resistance 33 is proportional tothe range.

A line 2i0 connects slider 34 with resistance 2li of another attenuator generally indicated at 2l2, resistance 33 of attenuator 30 being connected' by a line 2|3 to the other side of resistance 2li of attenuator 2 i2.

Attenuator 242 includes a slider 2I4 adapted to slide along resistance 2H, and this slider is manually adjustable in accordance with a reading taken from the airplane's altimeter. A line 35 is connected to slider 244, while a line 36 is connected to resistance 2li of attenuator 242, and as will now appear. the voltage across lines 35 and 36 is the generator output modified in accordance with the range and altitude, and hence is proportional to the lead necessary to correct for relative motion between gun and target. Line 35 is connected to a self inductance or the like. such as a choke coil 3l, this coil being connected by a line 38 to one side of a galvanometer generally indicated at 39. The armature of the galvanometer has mounted thereon a. post 40 from which extend arms 4i and 42, to the free ends of which is connected a horizontal cross hair 43. Upon energization of the galvanometer, cross hair 43 moves in a vertical plane to indicate vertical deilection in proportion to the voltage of the vertical deflection circuit.

2. Traiectory.-Line 36 is connected to a line 44, in turn connected to the slider 45 of an attenuator generally indicated at 46. Attenuator 46 has a resistance 4l over which slider 45 is positionable in accordance with variations in the zenith position of gun 20, movement of which causes movement of slider 45, as will be more particularly described hereinbelow. Terminal 48 of resistance 4l is connected by a line 49 to a slider 50 of an attenuator generally indicated at 5i. and having a resistance 52. This attenuator is similar to attenuator 30. and its slider arm 50 is connected to slider arm 34 of attenuator 30, so that manual 'adjustment of the range finder is reflected in movement of arm 50 along resistance 52.

Attenuators 5i and 46 are supplied with current by a battery 63. Hence, it will appear that the output of attenuator 5i is connected to attenuator 46, and the product of the outputs of both is added to the voltage across lines 35 and 38. The total voltage thus ilows through a line 54 connected to attenuators 46 and 5i and battery 53. and hence the added voltage across lines 44 and 54 is proportional to the range and to the drop of the bullet from its projected line of tire. excluding windage effects.

3. Bullet jump-Line 54 is connected to a line 55, in turn connected to a slider 215 adapted to ride over the resistance 2i6 oi an attenuator generally indicated at 2H. Slider 2I5 is adjustable in accordance with a reading from the airplanes altimeter, and is preferably mechanically linked, as indicated by the dotted line |35, to altitude attenuator 2|2. Resistance ZIE oi attenuator 2|1 is connected by a line 2I9 to the slider 55 of an attenuator generally indicated at 51. Attenuator 51 includes a circular resistance 58 having a terminal 59 connected by a line 59 to a slider 6| adapted to slidably engage a resistance 52 of an attenuator generally indicated at 53. One side of resistance 62 is connected by aline 54 to one side of battery 53, the other side oi the battery being connected to a line 65 connected to the side of resistance 62, and also to a terminal 66 on resistance 59 of attenuator 51. A voltmeter 61 is connected to lines 60 and B5 across battery 53, and is 4calibrated in miles per hour, so that slider 6I of attenuator 53 may be accurately adjusted to render the output of attenuator 53 proportional to indicated air speed. Slider 55 of attenuator 51 is mechanically or otherwise connected, as will be described in detail below to gun 20, or it is mounted in such a fashion that horizontal movement of the gun effects movement of slider 55, so that the resistance 58 of attenuator 51 is modied in accordance with the component of horizontal gun deilection. As the gun is usually positioned to nre from either the port or starboard beam of the airplaine, attenuator 51 is of a character as to reverse the current flow therefrom in accordance with the direction of fire of the gun. Thus, attenuator slider 56 is also connected to a line 2|9, in turn connected to the other side of resistance 2|6 of attenuator 2|1. This latter side of resistance 2I5 is connected to a line 69, so that the additional voltage across lines 55 and 68 is proportional to the vertical component of bullet lump, the value of which is determined by indicated air speed, azimuth position of the gun, and altitude. In this connection it should be noted that when'the gun is ring directly fore or aft in 'a horizontal plane, there is no vertical component of bullet jump or, for that matter, any horizontal component. Hence. when the gun is ring fore or aft. attenuator slider 56 would horizontal, as viewed in Figure 1, so that theproduct of the output-s of attenuators 51 and 63 is zero.

4. Windage.-Line 69 is connected to a line 69. in turn connected to a slider 10 of an attenuator generally indicated at 1|, having a resistance 12 connected by a line 13, in turn connected to a slider 14 of another attenuator generally indicated at 15. Resistance 16 of attenuator is connected by a line 'Il to a slider 18 adapted to slide about a resistance 19 of an attenuator generally indicated at 80. Resistance 19 and the last-referred to attenuator is connected by a line 9| to the slider 82 oi another attenuator generally indicated at 83, and having a resistance 84. Resistance 84 of attenuator 83 is connected by a line 85 to a slider B6 of an attenuator 81, whose resistance 88 is connected by a line 89 to one side of battery 53. The other side of battery 53 is connected by a line S0 to the other side of resistance 88, and also to resistance 84 of attenuator 93. A line 9| connected to slider 02 of attenuator 83 is also connected to resistance 19 of attenuator 80, and the slider 1B of this latter resistance is connected by a line 92 to resistances 16 and 12 o attenuators 15 and 1|, respectively. The resistance -of attenuator 1I is manaully adjustable in accordance with a reading from the altmeter (not shown) on the airplane, and hence its resistance is proportional to altitude. The resistance of attenuator 15 is adjusted upon adjusting the range iinder, and hence its resistance is proportional to range Attenuator l5 is mechanically connected te attenuators 30 and 5l, |21 and |00, the five attenuators operating together as indicated by the dotted line 93.

Attenuator is connected mechanically or otherwise to gun 20 so that its resistance is varied as the zenith position of the gun is varied. Attenuator B3 is, as noted above with respect to attenuator 51, adjusted upon horizontal movement of the gun. while attenuator 81 is set in accordance with indicated air speed as read from voltmeter 61 connected across battery 53. Hence it will appear that the added voltage across lines |59V and 92 is modied in accordance with indicated air speed, azimuth position, zenith position, range and altitude, all of which determine the value oi the factor of windage.

Line 92 is connected to the other side of galvanometer 39, and it accordingly will appear that the voltage across lines 38 and 92 is proportional to the vertical components of relative motion, trajectory, bullet jump and windage.

Before going into the description of the horizontal deflection circuit, it should be noted in connection with attenuators 80 and 83 that the output of attenuator 80 is reversed as the gun swings past the horizontal, whereas the output of attenuator B3 is reversed as the gun swings fore or aft of its dead abeam position. It should further be noted that the output of attenuator 80 is zero when the gun is ring in a horizontal plane, as there is no component of vertical detlection in so far as windage is concerned, when the gun is laid horizontally. Also, when the gun is tiring dead abeam on either side of the airplane, the output of attenuator 83 is zero as there is no component of vertical deiiection when the gun is ring dead abeam. Preferably. the vertical deection circuit is provided with a manually operable switch 94| which can be opened by the gunner when the gun is not in use, to preserve battery 53.

Preferably we provide another manually operated switch, such as switch 95 in line 92, which may be opened when desired to deenergize the entire vertical deilection circuit so that the gun may be aimed and red Without reference to the automatic gun sight.

Horizontal deflection circuit 1. Relative motion- Generator 21, which generates current upon horizontal movement of gun 20, is connected by lines 95 and 91 to the ends of a resistance 99 of an attenuator generally indicated at 99. This attenuator includes a slider |00 which, through the mechanical linkage indicated by dotted line 93. is adjustable along resistance 98 in accordance with adjustment of the range nder, so that the output of attenuator 99 is propcrtional to range. Slider |00 is connected by a line ||l=| to the resistance |02 of another attenuator generally indicated at |03, resistance |02 also being connected to line 91. Attenuator |03 includes a slider l 04 which, through the mechanical linkage indicated b'y dotted line |05, is connected to the sliders of attenuators 46 and 80. Accordingly. the resistance of attenuator |93 is varied in accordance with movement of gun 20 ln vertical planes. Attenuator slider |04 is connected to a line 220, in turn connected to a resistance 22| of an attenuator generally indicated at 222, the slider 223 of which is connected to a line |06. The other side of resistance 22| of this attenuator is connected by a line 224 to line 91, line 224 also being connected to a line 225, and hence the voltage across lines 225 and |06 is the output of generator 21 as modified in accordance with range, zenith position and altitude. which together determine the value of the horizontal component of lead due to relative motion.

2. Bullet jump-To compensate for the horizontal component of bullet jump, current is added to the horizontal deflection circuit from battery 53 by way of lines |01 and |00, the former being connected to line |06. Battery 53 is connected by lines |09 and ||0 to the resistance of an attenuato;` generally indicated at I2. having an adjustable slider ||3 adapted to be hand set in accordance with indicated air speed, as described above in connection with attenuator 53, Slider ||3 is connected by a line ||4 to one terminal of a resistance ||s5 of an attenuator generally indicated at H6, resistance |I5 also being con nected to line I I0. Resistance IIS is varied by a slider I1 which is linked mechanically or otherwise to the sliders of attenuators 51 and B3. so that the resistance of attenuator I I6 is determined by the azimuth position of the Gun.

Slider I1 of attenuator l0 is connected by lines ||8 and IIS to the resistance |20 of an attenuatcr generally indicated at I2 which has a slider |22 mechanically linked to the sliders of attenuators 46, 00 and |03, as indicated by dotted line |05, so that the resistance ot attenuator |2| is determined by the zenith position of the gun. Slider |22 of attenuator |2| is connected by-a line 226 to the resistance 221 of an attenuator generally indicated at 22B, the slider also being connected to the other side of this resistance by a line 229. Attenuator 228 includes a slider 230 which is preferably mechanically linked, as indicated by line |35, to the other altitude attenuators. so that adjustment thereof as heretofore described adjusts altitude attenuator 228. Resistance 221 of the latter attenuator is also connected to line |01. The added voltage across lines |01 and |08 is accordingly modied in accordance with indicated air speed. azimuth position, zenith position and altitude, which together determine the value of the horizontal component of bullet Jump.

It should be noted, in connection with this portion of the circuit, that the output of attenuator |I6 is zero when the gun is ring dead abeam, as in this position there is no horizontal component of deilection in so far as bullet jump is concerned. Also, the output of attenuator |2| is zero when the gun is firing in a horizontal plane, regardless of direction, as again there can then be no horizontal component of deflection in connection with bullet jump. It should further be noted that the outputs of attenuators IIE and |2| are reversed respectively as the gun swings past the dead abeam position, or passes from above to below the longitudinal axis of the plane, or vice versa.

3. Windage.-The horizontal deection circuit voltage is further modlied by the addition thereto of current from battery 53 connected to the circuit by lines |23 and |24, the former being connected to line |00. This additional current is controlled as to value by attenuators whose resistances are adjusted in accordance with indicated air speed, azimuth position, range and altitude, these attenuators being indicated generally at |25, |26, |21 and |23, respectively. Their respective sliders are connected with the sliders of the attenuators of similar type, as described above. Thus, slider |25a of the IAS attenuator |25 is connected as by mechanical linkage, indicated by dotted line |20, to attenuators 63, 01 and 2, all of these attenuators accordingly being manually adjusted until the voltmeter 51 connected thereacross gives a reading equal to the indicated air speed of the airplane. Slider |30 of attenuator |25 is connected to the sliders of attenuators 51, 83 and ||6 as by mechanical linkage indicated by the dotted line |3|, all of these attenuators being adjustable upon movement of the gun horizontally. Slider |32 of attenuator |21 is connected to the other attenuators, adjusted upon adjustment of the range finder through the mechanical linkage indicated b'y dotted line 33. Similarly, slider |34 or attenuator |28 is connected by mechanical linkage indicated by the dotted line |35 to slider 10 of attenuator 1| so that all of the altitude attenuators are adjusted simultaneously from a reading taken from the airplanes altimeter. Hence it follows that the modification of the voltage added to the horizontal deection circuit across lines |23 and |24 is in accordance with indicated air speed, azimuth position of the gun, range and altitude, which determine the horizontal component of windage.

In connection with attenuator |26, it should be noted that the output thereof is zero when the gun is firing directly fore or aft. as under such circumstances there is no horizontal deflection in so far as windage is concerned. Furthermore, the output of this attenuator reverses as the gun is swung from port to starboard, or vice versa. The horizontal detiection circuit, furthermore, can be completely deenergized through manual operation of a switch |36, which may be connected to line |24.

Line 225 is connected to a choke coil |31, in turn connected by a line |33 to one side of a galvanometer generally indicated at |39. Line |24 is connected to the other side of galvanorneter |39. The galvanometer armature is connected to a post |40, from which extend arms |4| and |42, to the free ends of which is connected a cross hair |43, which extends vertically and indicates horizontal deiiection as the galvanometer energization varies.

It will now appear that cross hairs 43 and |43, the positions of which are controlled respectively by galvanometers 39 and |39, comprise the reticle hereinbefore referred to, which is visible in a focal plane of the range iinder, all as will be described in detail hereinbelow.

From the above description of the vertical and horizontal deflection circuits, it may be seen that as the gunner trains his sight on the target, he must move both his range finder and gun, as the target moves, in order to keep the line of sight on the target. This movement, of course, operates generators 25 and 21. resulting in the energization of the two circuits which, of course, causes movement of the reticle formed by cross hairs 43 and |43. As pointed out above, the line of sight deviates from the line of lire. and this results because of the modiiications to the dencetion circuits which are made to compensate for the factors of relative motion, trajectory, bullet jump and windage. Hence, when the gunner has his line of sight on his target, his line of fire deviates therefrom by an amount sufficient to properly lead the target so that bullet and target meet.

It will also appear that as the sight and gun are moved, angular velocities are imparted to the line of sight and line of re, which are constant so long as the angular velocity of the gun remains constant. When, however, the guns angular velocity accelerates, the value of the voltages in the deflection circuits is increased, and this increase would cause the line of sight and line of fire to deviate, in eiect causing the line of sight to move relative to the line of fire in a direction reverse to that of the line of fire. If this condition were not corrected, it would not be possible for the gunner to get his line of sight on his target. To counteract this action of the line of sight, a counter E. M. F. is introduced in each of the circuits, and this counter E. M. F. is proportional to the rate of change of angular velocity of the gun. Choke coils 31 and |31, in Figure l, being of proper characteristics, introduce in each of the circuits the proper counter E. M. F. to counteract the relative backward movement of the line of sight from the line oi' re, upon an acceleration in the angular velocity of the line of nre.

While the horizontal and vertical deflection circuits shown in Figure 1 are series circuits, the various groups of compensating attenuators may be connected in parallel, Furthermore, where there are in one circuit a substantial number of attenuators having variable resistances, itv is preferable that each attenuator be of the so-called T-pad" type. as will be described below, by the use of which the desired results are attained without varying the total circuit resistance. To

this end, we have provided the vertical and horizontal deflection circuits shown in Figure 2, wherein the same number and grouping of attenuators are used as in Figure l, but the groups are connected in parallel, and the individual attenuators are of the T-pad type.

Vertical deflection circuit With reference to Figure 2, generator 25 (the vertical deflection generator) is connected by wires |44 and |45 to the input terminals |46 and |41 of an attenuator of the T-pad type. generally indicated at |48. Attenuator |48 includes a variable resistance |49, connected -across generator 25, a pair of fixed series resistances |50 and |5|, and a variable resistance |52, shunting fixed resistances |50 and |5|. attenuator or T-pad |48 may include one or more fixed balancing resistances, such as resistance |53. Variable resistances |49 and |52 are provided with contact sliders |54 and |55, so associated with their respective resistances that the output of attenuator |46 across its output terminals |56 and |51 may be varied without varying the total resistance of the circuit.

Attenuator output terminals |56 and |51 are respectively connected to lines 230 and 23|, in.

turn connected to the input side of an attenuator generally indicated at 232. This attenuator is also of the T-pad type, and accordingly is capable of a variable output without causing a change in the total circuit resistance. Attenuator 232 is manually adjusted in accordance with a reading from the airplane altimeter, and its output side is connected to lines |58 and |59. Line |58 is connected to one terminal |60 of a self inductance generally indicated at |6|, the other terminal |62 of which is connected by a line |63 to one side of galvanometer 39. Inductance I6! is provided for the same purpose as choke coil 31 (Figure l), i. e. to introduce into the circuit a counter E. M. F. which is proportional to the rate of change or the acceleration of the angular velocity of the line of sight as hereinbefore described. Inductance |6| preferably includes a balancing fixed resistance |64. connected to a variable resistance |65, in turn connected to a coil |66, the coil being connected to inductance terminal |62. Also connected to inductance terminal |62 by a line |61 is a contact arm |68 adapted to selectively engage one of several coil taps |69. Resistance |65 is provided with a slider |16 which varies the resistance of resistance |65 with respect to that of coil |66, as -contactor |68 engages one or another of coil taps |69, so as to maintain the total resistance of inductance |6| constant. Slider |10 and contactor |68 are mechanically linked so as to be capable of the stated operation. Also, slider |10 is mechanically linked as indicated by the dotted line |1| to sliders |55 and |54 of attenuator |48. Linkage I1| is connected with the manual adjustment on the range finder, as described below, so that when the gunner adjusts his range finder he automatically adjusts attenuator |48 so that the output thereof as across lines |58 and |59 is proportional to lead due to relative motion, the value of which is determined by range and altitude. Thus the line of ilre is corrected for the factor of relative motion.

The vertical deilection circuit output is further modied by the addition thereto of current. which additional current is in turn modied in accordance with the factors of trajectory, bullet jump and windage, in much the same manner as that described above in connection with Figure l. Thus, to provide vertical deflection to compensate for trajectory, we provide a pair of attenuators generally indicated at |12 and |13, the product of the outputs of which is carried by lines |14 and |15 to lines |16 and |11. The output of these attenuators is supplied from a battery 233 across which the attenuators are connected. These latter two lines connect respectively with lines |53 and |50, and accordingly feed into galvanometer 39. Attenuator |12 is connected by the mechanical linkage |1| with attenuator |48, and accordingly is operated therewith upon the gunners manipulation of his range finder. Attenuator |13 is mechanically linked to gun 20, for example, as by mechanical linkage indicated by the dotted line |10, so that movement of the gun in vertical planes varies the resistance of attenuator |13.

To compensate for bullet jump, additional current is fed into lines |58 and |59 from a battery 234 through lines |19 and |60. which are respectively connected to lines |16 and |11. The value of the current across lines |19 and |80 is modified in accordance with indicated air speed, azimuth position and altitude, respectively by attenuators generally indicated at IBI, |82 and 235. Attenuator |62 is connected to attenuator 235, in turn connected to lines |19 and |80, preferably by a reversing switch |83, so that the output of the attenuator may be automatically reversed in direction when the gun swings from port to starboard, or vice versa. The output from attenuator |82, being related to the azimuth position of the gun is, of course, zero when the gun is firing fore and aft, as in that position there is no vertical component of bullet jump.

Still further current is fed into lines |58 an |59 from battery 235 by way of a pair of lines |84 and |85 connected respectively to lines |16 and |11. The value of the current across lines |84 and |85 is a function of indicated air speed,

azimuth position, zenith position, range and altitude, the compensations necessary for these factors being determined by the attenuators generally indicated at |86, |81, |88, |09 and |00. Attenuator |86 is similar to attenuator IBI, being connected thereto as by a mechanical linkage indicated by the dotted line |9|, this mechanical linkage being manually operable by the gunner in accordance with the indicated air speed of the airplane. The azimuth position attenuator |81 is mechanically connected to attenuator |82 as by a mechanical linkage indicated by the dotted line |92, so that the two attenuators are adjusted together upon horizontal movement of the gun. The output of attenuator |81 is shifted in direction when the gun swings past dead abeam position, by a reversing switch |03 which connects the azimuth position attenuator |81 to the zenith position attenuator |88; The latter attenuator is similar to attenuator |13, and is mechanically linked thereto by linkage |13 so as to be adjusted therewith upon vertical movement of gun 20. As gun 20 is capable of shooting both above and below the horizontal axis of the airplane, the output of zenith position attenuator |88 must be reversed when the gun swings from above the axis to a point below it, and to this end a reversing switch |94 is provided.

Reversing switch i94 connects attenuator |80 with attenuator |89. the resistance of which latter attenuator is adjusted with that of attenuator |48 upon manual adjustment of the range nder. These two attenuators are mechanically linked by linkage l1 I. The resistance of the altitude attenuator |90 is varied manually by the gunner in accordance with a reading taken from the airplane altimeter, the adjustment being effected by suitable mechanical linkage, as indicated by the dotted line |95.

From the above, it will appear that the various compensations for the vertical components of deiiection of the factors of relative motion, trajectory, bullet jump and windage, are introduced into the vertical deflection circuit of Figure 2, by the several attenuators. It will further appear that as these attenuators are of the T-pad type, variation of their resistances does not result in a variation in the total circuit resistance. Furthermore, as the total circuit output is modified by the action of inductance IBI, as described, the current impressed on galvanometer 39 results in a deflection of cross hair 43, which causes a vertica1 deflection of the line of fire suilicient to impart the necessary vertical component of lead to the gun with respect to the target.

Horizontal deflection circuit As noted above with respect to the description of the horizontal deflection circuit of Figure l, there are horizontal components of deection in connection with the factors of relative motion between gun and target, bullet jump and windage, which must be imparted to the line of fire if it is to lead the target correctly, or, stated another way, the horizontal components of relative motion, bullet jump and windage must be allowed for, if the gun is to be correctly aimed. To this end, we have provided the horizontal deection circuit shown in Figure 2, wherein the vertical cross hair |43, controlled by galvanometer |39, is deflected by an amount proportional to the horizontal component of angular velocity of the gun, modified by the horizontal components of relative motion. bullet jump and windage. As these modifications are effected in the circuit of Figure 2 in substantially the same manner as described above in connection with the horizontal deilection circuit in Figure 1, it will suflice to say that the relative motion compensation results from the adjustment of range, zenith position and altitude attenuators |98, |91 and 231; bullet jump compensation is eiected through the adjustment of indicated air speed, azimuth position, zenith position and altitude attenuators |98, |99, 200 and 238, respectively, windage compensation being effected by indicated air speed, azimuth position, range and altitude attenuators 20|, 202, 203 and 204, respectively. The group of relative motion attenuators |98, |91 and 231 modify the output of generator 21, the group of bullet jump attenuators |98, |99, 208 and 238 modify the additional current from battery 239, while the windage attenuators 20|-204 modify a further addition of current from battery 240. All of these attenuators are, of course. preferably of the T-pad type, such as hereinbefore described, and accordingly the variations in their resistances have no effect on the total circuit resistance, which remains constant. The horizontal deflection circuit also includes an inductance 205, similar to inductance |6| to correct for rate of change of the horizontal component of angular velocity of the line of fire. It will now appear that the vertical and horizontal deection circuits of Figure 2 react in substantially the same manner as those in Figure 1, to correctly deviate the line of nre from the line of sight so that the gunA leads the target by a correct amount.

As pointed out hereinabove, inductances |6| and 205 are provided to vary the outputs of their respective circuits so that the deviation of the horizontal and vertical cross hairs will be corrected for the error introduced by the rate of change of the angular velocity of the line of fire. It should be noted in this connection, however, that in the place of these inductances (not shown) suitable transformers may be used to attain the desired end. Such a transformer would include a primary coil connected in the particular circuit involved, and a secondary coil (not shown) connected to a coil provided in the gaivanmeter which would when energized introduce a torque counter to that resulting from energization of the main circuit. Where such a transformer is used, it is desirable to connect into the circuit connecting the secondary coil with the counter torque galvanometer coil, a suitable attenuator similar to the T-pads shown in the circuits of Figure 2, so that the output of the transformer secondary could be modified in accordance with time of bullet flight as determined by range and altitude.

It will be noted that in the description of the circuits shown in Figure 2, we have assumed that the voltages of the several batteries would be fixed and constant in value. If the actual voltage varies, however from the desired value, suitable voltage controls must be introduced into the circuits to vary the voltages as desired. A voltmeter or other suitable indicating device may be provided to indicate that these controls are set at the proper value.

Referring now to Figures 3 and 4. wherein there is shown a gun and attached sight. which are used in conjunction with the control circuit shown in Figure 2, gun 20 includes a body portion 250, from which extends gun barrel 25|, and which also has secured to the rear end thereof suitable gun manipulating handles 252 or the like. Gun bodyr 250 is pivoted to support 22 to permit movement of the gun in vertical planes, all as will be described in detail hereinbelow. Support 22 is secured to and extends from a relatively heavy casting 253, which is preferably integrally formed with a base ring 254, on which walls 255 of a turret generally indicated at 256 are secured.

A ring 251, preferably L-shaped in cross section, is secured to the airplane fuselage structure (not shown) and has suitable surfaces to provide tracks for the support of anti-friction devices 256 connected to turret ring 254. This turret 256 is rotatable relative to ring 256 and to the airplane. Walls 255 (Figure 4) of turret 256 are indented as at 256 and 266 to provide suitable bearing mounts for bearings 26| and 262, respectively. These bearings rotatably support the opposite ends of a range finder, generally indicated at 263, provided with an eye piece 264 and conventional viewing windows 265 and 266. These viewing windows are conveniently positioned within the indentations in turret wall 255. A bracket 261 is suitably secured to the central portion of the barrel 266 of range nder 263, and extends therefrom in the direction of gun barrel 25| (see Figure 3). The forward end of bracket 261 is pivotally connected as by a link 266 to a portion or extension of the gun mount, as indicated at 566. As shown in Figure 4, range nder' barrel 266 rests on bearings 26| and 262. Hence, pivotal movement of gun 25| results in pivotal movement of range finder 263 in such a manner that the longitudinal axes of the line of fire of the gun and the optical axis oi' the range finder are always parallel.

As shown in Figures 12-14, range finder barrel 268 of range finder 263 preferably comprises an outer tubular casing 216 (Figures l2 and 14) within which a rectangular tube 21| is mounted. In so far as the optical system in range nder 263 is concerned, conventional lens and prism systems may be used, but for varying the focus of the range finder we prefer to employ a lens system such as is generally indicated at 212 in Figure 14. Lens system 212 comprises a supporting frame 213 or thelike, which is reciprocable longitudinally of rectangular tube 21| along guide tracks 214 and 215 mounted within the tube. A lens 216 is suitably mounted within frame 213 so that upon reciprocation of the frame, the position of the images at the focal plane of the range finder may be varied. A rack 211 is secured, as by a screw 216 to lens frame 213, and is sufficiently long to accommodate the full range of adjustment of lens 216. The teeth formed on the upper edge of rack 216 mesh with those of a gear 216 connected to a stud 266 or the like journaled in a bearing 26| connected to the side of rectangular tube 21|. Stud 266 also has secured thereto another gear 262, the purpose of which will be described hereinbelow.

Attached to stud 266, in any suitable manner, is a flexible cable 263 which extends through a. housing 284 secured to range nder barrel 266 to a point adjacent gun handles 252, where it is secured to gun body 256 by a bracket 265. The free end of cable 233 has secured thereto a control handle 56| readily accessible to the gunner's fingers when he is grasping gun handles 252, and by which the gunner can adiust the range finder, i. e. as the gunner rotates handle 56|, its rotation is imparted by way of flexible cable 263 (Figure 14) to gear 216 (Figure 14) which reclprocates rack 211 and accordingly lens 216.

Preferably, to the right hand end of range finder 263, as viewed in Figure 4, is secured galvanometer |36 (Figure 12). Galvanometer 36 is similarly secured to the range finder barrel, but to the left-hand end thereof between lens system 212 and viewing window 265. As these galvanometers are identical in construction, galvanometer |36 only will be described. Thus, galvanometer |36 includes a casing 286 which houses conventional galvanometer structure 261, from which extends the galvanometer armature 266 (Figure 13), carrying a needle or arm 266. A post |46 with its arms 14| and |42 and vertical cross hair |43 is secured to galvanometer needle or arm 266 so that the galvanometer deflection is imparted to the cross hair |43 when the galvanorneter is energized. Galvanometer 36 (Figure 4) similarly controls the deflection of the horizontal cross hair 43. Each of cross hairs 43 and |43 lies in a focal plane of the range iinder so that to the eye they comprise the cross hairs of a reticle.

It will now appear with respect to Figure 4 that as the gunner adjusts range iinder 263 through manipulation of h'andie or lever 56|, the images of the target are brought into coincidence in the area of movement of the reticle formed by cross hairs 43 and |43.

As noted hereinabove, gun 26 is mounted for pivotal movement in vertical planes within turret 256 (Figure 3). A bracket 266 is secured to the front end of gun body 266, a similar bracket 26| being secured thereto a suitable distance rearwardly of the front end of the gun body. Each of these brackets has pins extending therefrom, such' as studs263 and 264 extending from opposite sides of bracket 266 as viewed in Figure 6. Studs 263 are secured to a side bracket generally indicated at 265, the upper end 266 of which is pivotably mounted on a pin 261 or the like which extends through the side bracket and is connected to a boss 266 formed on the upper end of one prong 266 of a yoke generally indicated at 366. Studs 264 of brackets 266 and 26| (see Figure 5) are secured to a side bracket generally indicated at 36|, disposed on the other side of gun body 256 (Figure 6). An upward projection 362 (Figure 6) of side bracket 36| is pivotably mounted on a pin 363 which extends therethrough, and which is secured to a boss 364 formed on the upper end of the other prong of yoke 366. Hence it will appear that bracket 266, and accordingly gun 26 is pivotable about the axes of pins 261 and 363, which are coaxial. Yoke 366 is secured to the upper end of support 22. which is fixed in so far as movement in a vertical plane is concerned.

Side bracket 265 includes a lower portion 366 (Figure 5) having a circular edge generated from the axis of pin 261 (Figure 6) this edge having gear teeth cut th'ereon. Thus, lower portion 366 of side bracket 265 comprises a gear segment. Gear segment 366 (Figure 6) meshes with the teeth of a pinion 361 which is mounted on a. shaft 366 housed in a gear casing 366 secured in any desired manner in fixed relation to gun 26. The ends of shaft 366 are preferably rotatably mounted ln anti-friction bearings disposed in opposite walls of gear casing 366 so that vertical movement of gun 26 causes gear segment 366 tc swing,

and thus impart rotation by way of pinion 361 to shaft 366. The right-hand end of shaft 366 has mounted thereon a large gear 316 which meshes with a small pinion 3|| mounted on shaft 3|2, rotatably iournaled in the walls of gear casing 366. Also mounted on shaft 312 is another gear 3I3 which meshes with a pinion 3 I4 secured to a sh'aft 3I5 also journaled in the walls of gear casing 309. Shaft 3I5 includes a slotted extension 3I6 which extends through a boss 311 projecting from the lower part of gear casing 363. Extending from boss 3|1 is a threaded reduction 316 on which generator 25 is mounted. If desired, additional suitable supporting brackets (not shown) for generator 25 may be provided. Shaft extension 3 I6 is connected to the armature shaft 3 |9 of generator 25 in conventional fashion.

It may now be seen that pivoting of gun about the horizontal axes of pins 231 and 363 results in operation of generator by reason of the driving connection between the gun and generator aorded by the gear train, consisting of gear segment 305, pinion 301, gear 3I6, pinion 3 I I, gear 3|3 and pinion 3|4. By reason of the dimensioning of the several gears and pinions in this train, substantial R. P. M. is imparted to generator 25, by relatively small angular movement of the gun. The current output of generator 25 is utilized, as described above in connection with the description of the vertical deilection circuit shown in Figure 2.

As shown in Figure 5, side bracket has secured thereto, so as to move therewith, a generally triangular shaped plate 320, this plate being secured to bracket 30| as by a post 32| (Figure 6). Plate 320 is held on the outer end of post 32| as by a nut and washer 322 so as to be spaced from bracket 30|, the space between the bracket and plate being provided for a purpose described below. A second post 323 is secured to bracket 30| and extends therefrom through the other end of plate 320 (Figure 5) to provide a second support for the plate, the plate being held thereon as by a nut 324 threaded on the free end of the post. A stud 325 is fixed to plate 320, and as shown in Figure 6, extends laterally therefrom a substantial distance. Ii desired, the end of post 325 may be provided with a cam roller adapted to ride within a slot 326 of plate 321 mounted in the bifurcated end of a, rod 323. Post 32| may, if desired, be provided with a cam roller, as at 323 (Figure 6) disposed between plate 320 and bracket 36|. Cam roller 323 is adapted to ride within a slot 330 (Figure 5) formed in a plate 33| mounted in the bifurcated end of a rod 332.

Rods 328 and 332 are slidably supported in a bearing 333' which is secured to and extends from yoke 360. The lower end of rod 323 is slidably supported in a bearing 334, and the lower end of rod 332 is slidably supported in a. bearing 335. It will now be seen, with reference to Figure 5, that as gun 26 is pivoted counterclockwise, for example, plate 320 and posts 32| and 325 also pivot. Post 325 accordingly rides along slot 326 in plate 321, and as it does so causes the plate and accordingly rod 326 to move axially. Axial movement is imparted in a similar fashion to rod 332.

Rod 326 has a number of gear teeth 323a cut therein, and these teeth mesh with Aa pinion 335 (Figure 6) mounted on the end of a shaft 331 (Figure 6) journaled in a bearing 333 formed on the end of a strut 333, secured to and extending downwardly from bearing 333. Shaft 331 is connected to the sliders of attenuators 206 and |83 (see also Figure 2) which. it will be recalled, are two of the zenith position attenuators in the horizontal and vertical deilection circuits.

The lower end of rod 332 (Figure 6) is provided with teeth 340 which mesh with a pinion 34| mounted on a shaft 342. Shaft 342 is connected to the slider arms of attenuators |13 and |31 (Figure 6) which, it will be noted, are the other two zenith position attenuators in the horizontal and vertical deflection circuits (see Figure 2). Thus, all of the zenith position attenuators are automatically adjusted in accordance with the attitude of gun 2l) about its pivotal axis.

Referring now to Figure 3, base ring 251 has secured thereto an internal ring gear generally indicated at 343, having formed thereon three levels of teeth as at 344, 345 and 346 (Figure 8). As shown in Figure 9, generator 21, which is the horizontal deflection circuit generator, is mounted on turret ring 254 so as to move therewith upon rotation of the turret. The generator armature shaft 341 is keyed to a shaft 346 which is rotatably mounted in suitable anti-friction bearings in the walls of a gear casing 349. The free end of shaft 348 carries a pinion 350 which meshes with a large gear 35| secured to a shaft 352, which is also journaled in anti-friction bearings mounted in the walls of gear casing 343. Shaft 352 has mounted thereon or integrally formed therewith a pinion 353 which meshes with teeth 345 of ring gear 343. Inasmuch as the gear train just described, together with gear casing 349, are all secured with generator 21 to turret ring 254, all of these parts move with the turret upon rotation thereof. Hence, when the turret is rotated, the armature of generator 21 is driven at a substantial rate of speed by reason of the gear train described. Thus the generators output is proportional to the angular velocity of the turret.

Mounted within turret 256 (Figure 4) is an instrument and control panel 354, one end of which forms the top wall of a gear casing generally indicated at 355 (Figure 8). A plate 356, secured in any suitable manner to panel 354 in spaced relation thereto, forms the bottom wall of gear casing 355. J ournaled in suitable anti-friction bearings mounted in the walls of gear casing 355 is a shaft 351 having secured thereto a pinion 358. This pinion is adapted to mesh with teeth 344 of ring gear 343, which teeth, it will be noted, are substantially spaced from one another. The lower end of shaft 351 carries a gear 353, which meshes with a, gear 360 mounted on the lower end of a shaft 36| journaled in bearings in the walls of gear casing 355. A pinion 362 is mounted on the upper end of shaft 36|, and meshes with a large gear 363 mounted on a shaft 364 journaled in bearings in the gear casing walls.

Pinion 365 is also mounted on shaft 36| be tween gear 360 and pinion 362, the teeth of pinion 365 being adapted to mesh with teeth 34B on ring gear 343. Teeth 344 occur about ring gear 343 in angularly spaced groups, each group of teeth extending through teeth 346 being similarly grouped, but being positioned between adjacent groups of teeth 344.

Thus, rotation of turret 256 causes rotary movement of gear casing 355 (Figure 8) so that the gear train in casing 355 operates in one direction when teeth 344 mesh with pinion 35B, the gear train operating in the opposite direction when teeth 346 engage pinion 365. Thus, for one direction of rotation of the turret, shaft 364 may rotate both counterclockwise and clockwise. Shaft 364 is connected to the sliders of the azimuth position attenuators |32, |81, 262 and |33 (Figures 2 and l1) whereby the resistances of these attenuators are adjusted in accordance with the azimuth position of the gun, the values of the adjusted resistances being determined to a 

